Winfried Remy

Fossil arbuscular mycorrhizae from the early Devonian

AbstractThe 400 million-year-old Rhynie chert has provided a wealth of information not only of early land plants, but also of the fungi that inhabited this paleoecosystem. In this paper we report t...

The Gametophyte Generation of Some Early Devonian Land Plants

We summarize the current information on gametophytic plants from the Lower Devonian that are represented by three types based on permineralizations in the Rhynie Chert, two of which are antheridial (Lyonophyton and Kidstonophyton) and one that is archegoniate (Langiophyton). Impression and compression remains attributed to Sciadophyton and Calyculiphyton also are interpreted as gametophytic, based on their similarity to the permineralized forms. All are axial structures, with some axes terminating in cup-shaped gametangiophores on or in which gametangia occur, and all exhibit preserved cuticles with stomata and conducting tissue. Similarity in epidermal and conducting cell characters serves as a basis for postulating sporophyte relationships for the Rhynie Chert gametophytes as follows (N-2N): Lyonophyton-Aglaophyton, Kidstonophyton-Nothia, and Langiophyton-Horneophyton. Comparison with bryophytes and tracheophytes shows that these forms exhibit unique combinations of characters. They are more advanced than bryophytes in some features but differ in conducting cell type from tracheophytes. Thus they may represent lineages distinct from either of these groups. Their construction indicates some degree of morphological similarity between haploid and diploid thalli in the life cycles of these entities, thus supporting to some extent an alternation of isomorphic generations and the homologous theory of sporophyte origin for land plants. Alternatively, these data may indicate the early establishment of axial gametophytic structures within the context of an antithetic theory of sporophyte origin.

New information on gametophytes and sporophytes of Aglaophyton major and inferences about possible environmental adaptations

Abstract Additional information on gametophytes and sporophytes of Aglaophyton major from the Early Devonian Rhynie chert leads to a much better understanding of many biological and ecological aspects of this early land plant. At least three early ontogenetic stages can be demonstrated, before aerial axes start to develop on the young gametophytes. Only the aerial axes show the essential features of a land plant (stomata, conducting tissue); the initial stages seem more likely adapted to shallow aquatic or edaphic humid than to fully terrestrial environmental conditions. Serial sections of aerial axes of gametophytes and sporophytes of Aglaophyton have yielded new histological and developmental features. These include cuticle structures, stomatal and substomatal features. A hitherto undescribed type of specialized cortical tissue, arrested apices, the formation of second-order axes and bulbil-like organs are documented. New observations on the development of rhizoidal bulges and wound-repair (including conducting) tissues complete this report. The new information provides additional evidence for life (competition) strategies in Aglaophyton , e.g. extensive renewing growth and vegetative propagation. It throws new light upon the adaptive behaviour of Aglaophyton , e.g. protection mechanisms against desiccation of aerial axes. It also illustrates considerable developmental biology of Aglaophyton .

DEVONIAN FUNGI: INTERACTIONS WITH THE GREEN ALGA PALAEONITELLA

This paper describes three new taxa of fossil aquatic fungi preserved in 400-million-year-old Lower Devonian Rhynie Chert. All of the fungal morphotypes are attached to cells of the green alga Palaeonitella cranii. Milleromyces rhyniensis is characterized by a holocarpic, epibiotic zoosporangium with an elongate discharge tube that penetrates the host cell wall; arising from the base of the sporangium is an extensive rhizoidal system. Stages in infection by presumed zoospores are documented. In Lyonomyces pyriformis the globose-pyriform thallus is embedded in the surface coating of the cell wall. At the base of each thallus is a single rhizoid. Krispiromyces is extramatrical, holocarpic, and characterized by a short beak-like discharge papilla. The rhizoidal system appears to be apophysate. Some of these fungi were probably saprobes, while others were deemed parasitic because of the extensive hypertrophy of some of the algal cells. Although not all life history stages are represented, the discovery of these Lower Devonian forms greatly expands our knowledge of the biology and diversity of aquatic fungi in an ancient freshwater ecosystem.